Dankeschön Malte,
fortunately my concern is not about german cops ;
I was just investigating how "LUMINANCE" [lux] is measured according to german standard StVZO---Straßenverkehrs-Zulassungs-Ordnung.
It appears that when a brochure says 10 lux, for example, that means 10 lux at 10 meters in front of the bike.
And that's enough for me
Bye
Conrad